1. Technical Field
Exemplary embodiments relate to memory devices, and more particularly to volatile memory devices, memory controllers, memory systems and a methods of refreshing volatile memory devices.
2. Discussion of the Related Art
A volatile memory device, such as a dynamic random access memory (DRAM), performs a refresh operation to retain data stored in memory cells. If a memory cell has a retention time shorter than a certain refresh period (often pre-defined as a standard), a row of memory cells including such a memory cell should be replaced with a row of redundancy cells. As the size of a memory cell shrinks, the number of memory cells having retention times shorter than a pre-defined or standard refresh period increases. Accordingly, the number of rows of redundancy cells of a conventional volatile memory device should be increased.